Viswanathan, who was born in India and spent most of her childhood years in Scotland, issued a statement acknowledging similarities between her book, How Opal Mehta Got Kissed, Got Wild, and Got a Life, and two works by a fellow New Jersey author, Megan McCafferty.
She insisted, however, that she did not copy McCafferty's work so much as unconsciously "internalise" it. She pledged to make revisions for any future printings of her novel.
"When I was in high school," she said, "I read and loved two wonderful novels by Megan McCafferty, Sloppy Firsts and Second Helpings, which spoke to me in a way few other books did ... I wasn't aware of how much I may have internalised Ms McCafferty's words ... I can honestly say that any phrasing similarities between her works and mine were completely unintentional and unconscious ... I sincerely apologise to Megan McCafferty."
The apology did not, however, appear to be the end of Viswanathan's troubles so much as the beginning. Her publisher, Little, Brown, which paid $500,000 (£280,000) for a two-book deal with Viswanathan, put out a separate statement describing the plagiarism accusation as "a serious matter" and saying it was conducting an investigation.
Lawyers for both Little, Brown and McCafferty's publishing house, Crown, were reported to be in discussions.
McCafferty said: "After reading the book in question, and finding passages, characters, and plot points in common, I am hoping this can be resolved in a timely and responsible manner."
The whistle was first blown on Viswanathan by the Harvard campus newspaper, The Crimson, which found 13 instances where the phrasing, ideas and language of Opal Mehta closely resembled passages from McCafferty's work. The newspaper had made little secret of its dislike of Viswanathan's book, suggesting that its account of an over-achieving Asian girl attempting to get into the most prestigious university in the country depicted Harvard in a clichéd and unhelpful light.
Further investigation by The New York Times, one of several publications examining the book, is said to have discovered a further 16 instances of similarity.
Although Viswanathan's book ostensibly has a very different plotline from Ms McCafferty's works, there are similarities of situation and character. Both Opal Mehta and McCafferty's heroine are high-achieving teenagers from New Jersey who fall for smart but badly behaved boys with very similar personal habits and clothing styles. According to The Boston Globe, both heroines refer to the school in-crowd as the "upper crust" and low-lifers as "dregs", and have near-identical cliques of friends.
For the moment, Viswanathan retains the support of her publisher and agent, both of whom said they were confident that the similarities were unintentional. More disturbing revelations have emerged, however, about the way the book was sold - via a book "packager" called 17th Street Productions, since renamed Alloy Entertainment, which helped her conceptualise and map out the plot.
Although there has been no suggestion that the actual writing was done by anyone other than Viswanathan, it is highly unusual for fiction to be packaged in this way - suggesting that the author was regarded as a marketing opportunity as much as a writer.
Publicity surrounding Viswanathan's youth, the big money she was paid and the movie deal she has reportedly signed with Steven Spielberg's production company Dreamworks have certainly boosted sales. The book is already number 32 on The New York Times's hardback best-seller list.
'I wasn't aware how much I may have internalised her words'
McCafferty: Marcus and I had never, ever acknowledged each other's existence before. So I froze, not knowing whether I should (a) laugh, (b) say something, or (c) ignore him and keep on walking. I chose a brilliant combo of (a) and (b). 'Uh, yeah. Ha. Ha. Ha.'
Viswanathan: Sean Whalen and I had never acknowledged each other's existence before. I froze, unsure of (a) what he was talking about, or (b) what I was supposed to do about it. I stared at him. 'Flatirons,' he said. 'At least seven flatirons for that hair.'
"Ha, yeah. Uh, ha. Ha."
McCafferty: Bridget is my age and lives across the street. For the first twelve years of my life, these qualifications were all I needed in a best friend. But that was before Bridget's braces came off and her boyfriend, Burke, got on, and before Hope and I met in our seventh-grade honors class.
Viswanathan: Priscilla was my age and lived two blocks away. For the first fifteen years of my life, those were the only qualifications I needed in a best friend. ... But that was before freshman year, when Priscilla's glasses came off, and the first in a long string of boyfriends got on.
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